That may not be on par with this year's roaring return but is still historically robust, he said, considering that 2013 has been an "extraordinary year" for stock gains.

In a "Squawk Box" interview, Siegel said that the Dow could finish out 2013 with another 6 percent, on top of the blue-chip index's 25 percent gain year-to-date.

"November and December are usually pretty good months," he said. "There's no major uncertainties that are hanging over the markets, at least in these two months coming up."

Barring a major selloff this week, the Dow, the S&P 500 and the Nasdaq will all be positive for September and October. That is relatively rare, happening only four other times in the past 30 years: 2010, 2007, 2006 and 1998.

Looking ahead, Siegel also said he sees GDP accelerating next year to "3 [to] 3.5 percent from the 2 percent we're stuck in this year." That will make for a very "good climate for earnings growth," he added.

"If we can get 3.5 percent GDP, the market can take a [Federal Reserve] tapering down to zero," he said. "Don't forget, the first rate hike is not expected—right now if you look at the futures market—until April or May of 2015."

The Fed is scheduled to begin its two-day October meeting Tuesday. After surprising Wall Street last month by not scaling back its $85 billion-a-month bond-buying program, it is not expected to take any action either this week or at its December meeting. Siegel said the first chance for tapering appears to be in March.

He also does not expect another government shutdown or a down-to-the-wire debt ceiling fight early next year, when the temporary deals to fund federal operations and extend the borrowing limit run out.

"I think they are going to kick the [budget] can down the road a whole year," Siegel said. "So that'll be off our plate and that will be a very, very positive factor [for] first-quarter 2014."